Why do some young adults today feel it necessary to totally forget about their parents once they become independent?

Is it just a phase they go through until they are more settled?
Or are they just selfish or too busy?
Can you ever be too busy to spare a few minutes worth of conversation at least once a week with your folks?
BTW, I don’t mean this question to be those who were neglected as children. I get turn about being fair play.
Is it just that our society is becoming more selfish or are parents just living too long and its time to put them on a raft and pushed out to sea because they are outliving their usefulness.